The present invention relates to an apparatus for detecting a state of a particulate filter for trapping particle matters in exhaust gas of an internal-combustion engine.
In general, an engine, in particular, a diesel engine exhausts particle matters (herein after referred to as “PM”) at its operation time. In order to prevent the PM from exhausting to the atmosphere, a particulate filter is provided in an exhaust system of the diesel engine. The particulate filter traps the PM when the exhaust gas passes through small holes in a wall of the filter toward adjacent passage.
Sometimes, the particulate filter may not be able to trap the PM due to some damage in the filter. In order to detect such a failure state, it is preferable that the state of the particulate filter be always estimated from sensor information.
The Japanese Patent Application Publication No. S57-159519 discloses a technique for determining clogging in the particulate filter by detecting a difference between pressures in upstream and downstream sides of the particulate filter and an exhaust flow amount. Determination of clogging is made based on the ratio of the two values.
Japanese Patent Application Publication No. H8-284644 discloses a technique for calculating an amount of PM accumulated in a particulate filter based on the difference between pressures in upstream and downstream sides of the particulate filter and a flow volume of exhaust gas. Based on the accumulated PM amount, time for starting a regeneration process on the particulate filter is determined. Also, failure of the particulate filter is determined based on change in time of the accumulated PM amount.
Characteristics of the state of the particulate filter appear clearly during transitional operation such as acceleration and deceleration. It is an objective of the present invention to provide a scheme for determining a state of a particulate filter during transitional operation of an engine.